Repairing painted surfaces requires that the repair paint visually matches the originally applied paint film. To this end, the colour of the original paint film is measured and subsequently a paint composition is determined having substantially the same colour within a predetermined tolerance. This can be done by searching a suitable paint composition in a databank or a suitable paint composition can be calculated based on the colorimetric data of the paint components.
To allow easy formulation of matching paints in any colour, toners are often used. Toners are compositions of base colours comprising all ingredients which make up a complete paint. These toners can be mixed to obtain a paint of a colour, which after being applied and dried as a paint film, matches the colour of the paint originally coating the substrate. Based on the colorimetric data of the individual toners, the colorimetric features of mixtures can be predicted by calculation, taking into account the concentrations of the toners used. Alternatively, paint compositions can be formulated on basis of other types of modules, such as pigment concentrates, binder modules, effect modules, components comprising flop-controllers, etc.
Besides colour, a paint film shows numerous further visual properties. Particularly when effect pigments, such as for example aluminum flake pigments or pearlescent pigments, are used, the look of a paint film is not of a uniform colour, but shows texture. This can include phenomena as coarseness, glints, micro-brilliance, cloudiness, mottle, speckle, sparkle or glitter. In the following, texture is defined as the visible surface structure in the plane of the paint film depending on the size and organization of small constituent parts of a material. In this context, texture does not include roughness of the paint film but only the visual irregularities in the plane of the paint film. Structures smaller than the resolution of the human eye, contribute to “colour”, whereas larger structures generally also contribute to “texture”.
Also particles which are not directly observable by themselves, can contribute to the overall visual appearance of a paint film. Des-orienters are an example of such particles. Effect pigments are generally flakes tending to take a horizontal orientation in a cured film. To prevent this, and to obtain more variation in flake orientation, spherical particles are used, referred to as des-orienters. Using des-orienters in a metallic paint, results in more glitter.
Hitherto, the texture of the paint film to be repaired was judged by the eye, e.g., by comparing it with samples on a sample fan. The results of such approach are strongly dependent on the skills of the practitioner and are often not satisfying.
In practice, a colour specialist wanting to match a textured paint, first selects one or more effect modules or toners to obtain a matching texture effect. Meanwhile or subsequently, colourant modules or toners are selected to obtain a colour match. The result is compared with the original paint and iteratively adjusted if correction appears to be necessary. Selecting the right effect modules is difficult and requires a trial and error approach or accurate computer analysis of the effect pigments in the paint to be matched.
EP-A 637 731 discloses a method for reproducing texture properties of a paint film. The reproduced paint is formulated on basis of concentrations of paint modules. The formulation is selected from a database or formulations with given texture properties. If this does not result in a satisfying match, corrections can be made by interpolation between two close matches.
WO 01/25737 discloses a method of combined colour and texture matching, using a digital imaging device, such as a CCD camera, to determine the texture.
A matching paint is determined by searching in a databank of colour formulations linked to texture data.
US 2001/0036309 discloses a method of measuring micro-brilliance and using it for matching a repair paint with an original paint on, e.g., an automobile. The method includes measurement of colour as well as micro-brilliance, a specific type of texture. A colour formula with a matching micro-brilliance is selected from a databank of paint formulas. Consequently, the obtained micro-brilliance texture is acceptably matching. However, the colour is not necessarily matching evenly well. Hence, the colour formula needs to be iteratively adjusted until the colour match is also acceptable. In this prior art system, colour formulas that initially do not have the right texture are not taken into consideration, although these formulas could still be viable candidates as a formulation to start with. Furthermore, this prior art method does not assure that the texture remains intact during the adjustments of the colour formulas.